This invention relates to cushion underframes for use on railway cars, that is, underframes which include a rigid draft and buffing or sliding sill, extending substantially the length of the car and attached at its ends to the car's couplers, the column being movable lengthwise against the resistance of cushion means when forces in buff and draft are applied to the couplers. More particularly, the present invention is concerned with a novel cushion underframe having substantially increased capacity when the magnitude of the shock forces generated during buff or draft conditions exceed a predetermined magnitude.
Cushion underframes have enjoyed wide spread and satisfactory use on various types of railway cars. Cushion underframes include a rigid draft and buffing column or sliding sill extending substantially the length of the car and attached at its ends to the couplers. The sliding sill is movable endwise against the resistance of cushioning means, when forces in buff and draft are applied to the couplers. Cushion underframes have enjoyed commercial success in association with railway car cabooses. When properly tuned, the cushion underframe absorbs the shock forces generated during draft and buffing operations and provides extremely smooth cushioning action at very low reaction to provide maximum comfort for the crew during normal operation of the rolling stock. However, when these cars are subjected to severe impacts, such as those that occur during switching operations, it has been found that the cushioning capacity of the underframe is insufficient to absorb the severe shock forces resulting in violent contact between the solid stops fixed to the sliding and fixed sills of the underframe thereby resulting in damage to these members.